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MDP Hydraulics
Features & Specifications |
1Stroke lengths to 4100mm(161 inches),Customizable |
Hydraulic pressure to 31.5 Mpa( 4568 psi), Customized up to 63Mpa (9137psi) |
Temperature to -20℃ to 80℃(-4'Fto 176°F),Customized up to 230℃(446°F) |
Standard Carbon, Alloy & Stainless material options available based on application |
Single & Double Acting configurations |
Plating/treatment options available based on application |
Seal options available based on fluid/pressure/temperature |
Special Options |
Chrome bore available Adjustable cushions |
Air bleeds Special materials & plating |
Integrated valve technology Linear displacement transducers |
Proximity switches Pressure boosters |
Intensifier designs |
The hydraulic piston double-acting cylinder is the core power execution component of the working device (arm, boom, bucket) of a backhoe excavator. It converts the high-pressure oil energy from the hydraulic system into precise and powerful linear reciprocating mechanical motion, directly driving a series of complex actions such as excavation, lifting, rotation and unloading of the excavator. Unlike single-acting cylinders, the double-acting cylinder is driven by hydraulic power in both the extension (push) and retraction (pull) directions of the piston, thus achieving precise and bidirectional control of the movement speed and position of the working device, and is a key component for ensuring the efficient, smooth and reliable operation of the excavator.
The internal structure of the double-acting oil cylinder is divided into two sealed chambers by the piston: the rodless chamber (the side where the piston rod is not extended) and the rod chamber (the side where the piston rod is located). Its working principle is as follows:
• Extension process (thrust): When high-pressure oil flows through the A oil port into the rodless chamber, and the oil in the rod chamber flows back to the oil tank through the B oil port, the liquid pressure acting on the large area of the piston pushes the piston rod to extend outward, generating a huge thrust, which is used to achieve actions such as excavation and lifting.
• Retraction process (pulling force): When the high-pressure oil passes through the B oil port into the piston rod chamber, and the oil in the non-piston rod chamber flows back to the oil tank through the A oil port, the liquid pressure acting on the annular area of the piston pulls the piston rod inward, generating a pulling force, which is used to achieve reset, re-capture of the bucket, and other actions.
By controlling the oil circuit switching through an external multi-way directional valve, the extension and retraction movement, speed and output of the oil cylinder can be precisely controlled.
To withstand the extremely harsh working conditions of the backhoe excavator (high impact, heavy load, muddy water environment), this cylinder is designed and manufactured with high-quality materials.
• Cylinder barrel: It is precisely forged from high-strength alloy steel (such as 27SiMn) and undergoes quenching and tempering treatment. The inner hole is processed by honing or rolling, achieving extremely high dimensional accuracy, geometric accuracy and surface finish (Ra ≤ 0.4 μm), ensuring smooth piston movement, low friction and long service life.
• Piston and Piston Rod: The piston is made of wear-resistant cast iron or steel and is equipped with high-performance combined sealing rings. The piston rod is made of medium carbon alloy steel (such as 42CrMo), and after quenching and tempering treatment, it undergoes hard chrome plating treatment (plating thickness ≥ 0.05mm), which has extremely high hardness (HV ≥ 750), excellent wear resistance and outstanding corrosion resistance.
• Sealing System: Utilizes specialized sealing components from internationally renowned brands (such as Parker, Hallite). These include piston seals (to prevent internal leakage), piston rod seals (to prevent external leakage), guide belts (to support the piston rod and prevent wear), and dust rings (to prevent dust and sand from entering). All sealing materials are capable of operating within a working temperature range of -30°C to +100°C and can withstand various hydraulic oil media.
• Guide sleeve and buffer device: A built-in wear-resistant bronze guide sleeve provides stable support for the piston rod. At the end of the stroke, an adjustable buffer structure is designed, which reduces the piston speed smoothly through the throttling principle, effectively eliminating terminal impact and protecting the cylinder and the mainframe structure.
• Installation accessories: Multiple installation forms are provided, such as ear-ring type (with joint bearings), flange type, and ear shaft type, to meet the different installation requirements of different hinge points on the arm, boom, and bucket of the backhoe excavator.
Product Features and Advantages
• Outstanding strength and durability: The key pressure-bearing components are made of high-strength materials and undergo strict heat treatment processes. The design has a high safety factor, capable of withstanding the intense impact loads and continuous alternating stresses encountered during excavation operations, and have a long service life.
• Extremely high operational accuracy and controllability: The double-acting hydraulic drive ensures rapid response and precise positioning for the extension and retraction actions. Combined with the pilot hydraulic control system, it enables precise micro-operation of the excavator, thereby enhancing operational efficiency and quality.
• Excellent sealing and leak prevention performance: A multi-layer and multi-material composite sealing solution ensures long-term reliable sealing under a system working pressure of up to 35 MPa, with minimal leakage, reducing hydraulic oil loss and maintenance costs.
• Strong environmental adaptability: The surface treatment and sealing materials can effectively resist the invasion of rainwater, sand, and corrosive media during outdoor operations. The special chrome plating process of the piston rod and dust-proof design are particularly suitable for continuous operation in harsh industrial and mining environments.
• Ensuring ease of maintenance: The modular design enables on-site replacement of key vulnerable components (such as sealing elements and guide sleeves), significantly reducing equipment downtime. The oil ports feature standard interfaces for easy connection.
On an excavator with a bucket arm, three sets of double-acting hydraulic cylinders are usually equipped, each controlling one of the three main joints:
1. The arm cylinder: Connected between the turntable and the arm. When extended, it lifts the arm and the entire working device at the front end; when retracted, it lowers the arm. It is the main mechanism for controlling the digging depth and unloading height.
2. The bucket arm cylinder: Connected between the arm and the bucket arm. When extended, it pushes the bucket arm and the bucket towards the body for excavation (bucket arm excavation); when retracted, it pushes the bucket arm and the bucket out.
3. The bucket cylinder: Connected to the bucket through a six-link mechanism. When extended, it rotates the bucket inward for "picking up" or "retracting"; when retracted, it rotates the bucket outward for "discharging" or "opening".
These three sets of cylinders work in coordination under the control of the hydraulic system, enabling complex spatial trajectory movements and achieving efficient earthwork operations.
When choosing or replacing the hydraulic cylinders for your backhoe excavator, please ensure the following key parameters:
1. Main unit model and interface size: Provide the brand and model of the excavator (such as Komatsu PC200-8, Caterpillar 320D), so as to match the original installation size, hinge hole spacing and oil port specifications.
2. Performance parameters: Confirm the cylinder diameter, rod diameter and stroke of the original hydraulic cylinder. The required thrust/tractive force must be determined based on the mechanical calculation of the working device of the excavator and must meet the digging force requirements of the bucket and boom specified by the host.
3. System pressure: Confirm the rated working pressure and peak maximum pressure of the excavator's hydraulic system. The rated pressure of the selected cylinder must be higher than the system's maximum pressure and leave a safety margin.
4. Working environment: If there are special requirements for operation in extremely cold, hot, coastal or corrosive environments, please explain in advance so that suitable sealing materials and surface treatment processes that can withstand low temperatures or corrosion can be selected.
• Installation: Before installation, ensure that all hinge pin holes are clean and undamaged. Use the appropriate tools to install the hydraulic cylinder in place and tighten the connecting bolts according to the specified torque. Before connecting the oil pipe, ensure that the oil ports are clean to prevent contaminants from entering the system.
• Usage: Avoid applying lateral forces or radial impacts to the piston rod of the hydraulic cylinder. Do not overload the cylinder beyond its rated pressure. During operation, carefully observe for any abnormal noises, vibrations or leaks.
• Maintenance:
Daily inspection: Check whether there are any scratches on the surface of the piston rod, whether the coating has peeled off, and whether there is any oil leakage at each connection point.
Regular maintenance: Follow the maintenance manual for the main unit to replace the hydraulic oil and filter elements regularly to keep the oil clean (it is recommended to reach NAS 9 grade or ISO 18/16/13 cleanliness standards). When storing for a long time, fully retract the cylinder and apply rust protection to the exposed parts of the piston rod.
Fault handling: Common faults include slow operation, lack of power (possible internal leakage), external leakage, crawling (possible intake or contamination) etc. When a fault occurs, it should be diagnosed and repaired by professionals, with a focus on inspecting the seals and guiding components.
